For instance, a liquid crystal display apparatus (an LCD), which is used as a display screen in a notebook-sized personal computer or a word processor, has a tendency to have a deteriorated display quality when it is viewed from a diagonal direction, because its optical anisotropy gives the LCD a narrower angle of visibility, compared to other display apparatus, such as CRT. Hence, for example, an LCD 501 described in Japanese Un-Examined Patent Publication Tokukaihei No. 5-113561 (published on May 7, 1993) is equipped with, as shown in FIG. 42, a liquid crystal cell 511, a liquid crystal compensation plate 514, which is disposed adjacent to the liquid crystal cell 511 for optically compensating the liquid crystal cell 511, λ/4 plates 513c and 513d, which are placed to sandwich the liquid crystal cell 511 and the liquid crystal compensation plate 514, and linear polarization films 512a and 512b, which are mounted to have both the λ/4 plates 513c and 513d in between. The respective λ/4 plates 513c and 513d have a retardation in an in-plane direction that are set at a quarter of transmitted light. The λ/4 plate 513c is prepared from a uniaxial material having a negative optical activity, while the λ/4 plate 513d is made from a uniaxial material having a positive optical activity.
In the above arrangement, light transmitted thorough the linear polarizing film 512a is converted into a circularly polarized light by the λ/4 plate 513c, then is introduced into the liquid crystal cell 511 via the liquid crystal compensation plate 514. Here, the liquid crystal cell 511 has a nematic liquid crystal which is aligned substantially vertically with respect to a substrate where no charge is applied therein. Therefore, the liquid crystal cell 511 has emitting light that is circularly polarized, which is substantially equal to the light introduced. The emitted light is converted into a linearly polarized light by the λ/4 plate 513d. Here, because both the linear polarization films 512a and 512b are placed so that absorption axes of the respective linear polarization films 512a and 512b cross each other at a right angle, the linearly polarized light is absorbed by the linear polarization film 512b, resulting in a black display. Moreover, even when the liquid crystal cell 511 gives a phase difference to the transmitted light coming from a direction angled from a substrate normal direction during the black display, the optical activity of the liquid crystal compensation plate 514, which is reverse to that of the liquid crystal cell 511, enables the liquid crystal compensation plate 514 to cancel out the phase difference, thereby extending an angle of visibility.
On the other hand, application of a charge causes liquid crystal molecules to incline horizontally with respect to the substrate, so that the emitted light from the liquid crystal cell 511 is elliptically polarized. Accordingly, the emitted light out of the λ/4 plate 513d is not entirely absorbed by the linear polarization film 512b, thus showing a white display.
However, in the above arrangement, both the λ/4 plates 513c and 513d require different manufacturing processes, respectively, by reason that their optical activities are different: one is positive and the other is negative. Thus, it is a problem for the above arrangement that it is difficult to uniform their in-plane retardation.
Here, if a difference is caused between their retardations, for example, by lack of uniformity between their respective manufacturing processes, a light leakage in a front direction is generated during the black display, thus deteriorating a contrast ratio in a front direction.
Furthermore, in the above arrangement, when a contrast ratio of a predetermined angle from the normal direction is measured for every in-plane directions, a peak of the contrast ratio often shows unevenness, thus making it hard to balance between viewing angle characteristics from an above position (or a bottom position) and those from a right position (or a left position).